Method for generating additive combinations of PCM voice samples

Abstract

A method for generating additive combinations of PCM voice samples separates the samples into magnitude portions and sign portions. The magnitude portion of each PCM voice sample is converted from compressed PCM form to linear form. The magnitudes of the two voice samples, in linear form, along with their respective signs are added together to form a resultant linear value. If there is any overflow as a result of the addition, the resultant value is truncated so as not to exceed a maximum allowable value. The resultant value is then converted from linear form to compressed PCM form along with the proper sign. These steps are iterated for each possible value of the input PCM voice samples. These resultant values are stored in a storage medium for rapid on-line use by a switching system. Off-line generation of combined PCM samples saves system real time as compared to generating these combinations on-line in real time.

What is claimed is: 
     
       1. A method for generating additive combinations of PCM voice samples, said method comprising: first initializing a first speaker index to a predefined value;   first obtaining a magnitude value of a first of said PCM voice samples;   first converting said magnitude of said first PCM voice sample from compressed PCM form to linear form;   second initializing a second speaker index to a predefined value;   second obtaining a magnitude value of a second of said PCM voice samples;   second converting said magnitude of said second PCM voice sample from compressed PCM form to linear form;   combining said linear forms of said first and second PCM voice samples into a third PCM voice sample in linear form;   third converting said third PCM voice sample from linear form to compressed PCM form;   outputting said third PCM voice sample in compressed PCM form to a suitable storage medium;   first incrementing said second speaker index value by one;   first iterating all said steps beginning with said step of second obtaining, if said second speaker index value is less than or equal to a predetermined value;   second incrementing said first speaker index value by one; and   second iterating all said step beginning with said step of first obtaining, if said first speaker index value is less than or equal to said predetermined value.   
     
     
       2. A method for generating additive combinations of PCM voice samples as claimed in claim 1, said step of outputting including the step of storing each of said third PCM voice samples in a location of a programmable read only memory indexed by said first and second speaker index values. 
     
     
       3. A method for generating additive combinations of PCM voice samples as claimed in claim 2, said step of first obtaining including the step of first separating said first PCM voice sample into a magnitude value portion and a sign value portion. 
     
     
       4. A method for generating additive combinations of PCM voice samples as claimed in claim 3, said step of second obtaining including the step of second separating said second PCM voice sample into a magnitude value portion and a sign value portion. 
     
     
       5. A method for generating additive combinations of PCM voice samples as claimed in claim 4, wherein there is further included the steps of: first determining whether said first and second sign value portions are equal;   first setting a sign value portion of said third PCM voice sample equal to said sign value portion of said first PCM voice sample;   second setting a magnitude value portion of said third PCM voice sample, in linear form, equal to said magnitude value portion of said first PCM sample, in linear form, minus a particular value, added to the magnitude value portion of said second PCM voice sample, in linear form, minus said particular value and added to said particular value; and   said steps of first determining, first and second setting being performed in response to said determination that said sign value portions of said first and second PCM voice samples are equal.   
     
     
       6. A method for generating additive combinations of PCM voice samples as claimed in claim 5, wherein there is further included the steps of: second determining whether said magnitude value portion of said first PCM voice sample is greater than or equal to said magnitude value portion of said second PCM voice sample;   third setting a sign value portion of said third PCM voice sample equal to the sign value portion of said first PCM voice sample;   fourth setting a magnitude value portion of said third PCM voice sample, in linear form, equal to said magnitude value portion of said first PCM voice sample, in linear form, minus said particular value, minus said magnitude value portion of said second PCM voice sample, in linear form, minus particular value, plus said particular value; and   said steps of second determining, third and fourth setting being performed in response to said determination that said magnitude value portion of said first PCM voice sample is greater than or equal to said magnitude value portion of said second PCM voice sample.   
     
     
       7. A method for generating additive combinations of PCM voice samples as claimed in claim 6, wherein there is further included the steps of: third determining whether said magnitude value portion of said first PCM voice sample is less than said magnitude value portion of said second PCM voice sample;   fifth setting said sign value portion of said third PCM voice sample equal to said sign value portion of said second PCM voice sample;   sixth setting a magnitude value of said third PCM voice sample, in linear form, equal to said magnitude value of said second PCM voice sample, in linear form, minus said particular value, minus said magnitude value portion of said first PCM voice sample, in linear form, minus said particular value, plus said particular value; and   said steps of third determining, fifth and sixth setting being performed in response to said determination that said magnitude value portion of said first PCM sample is less than said magnitude value portion of said second PCM sample.   
     
     
       8. A method for generating additive combinations of PCM voice samples as claimed in claim 7, wherein there is further included the steps of: fourth determining whether said magnitude value portion of said third PCM voice sample, in linear form, is greater a the maximum allowable value;   seventh setting said magnitude value portion of said third PCM voice sample, in linear form, equal to said maximum allowable value in response to said determination that said third PCM voice sample exceeded said maximum allowable value; and   said steps of fourth determining and seventh setting being performed in response to said steps of second setting, fourth setting and sixth setting.   
     
     
       9. A method for generating additive combinations of PCM voice samples as claimed in claim 8, wherein there is further included the step of second combining said sign value portion of said third PCM voice sample with said magnitude value portion of said third PCM voice sample in compressed PCM form, said step of second combining being performed in response to said step of third converting. 
     
     
       10. A method for generating additive combinations of PCM voice samples as claimed in claim 9, said particular value being equal to the value of 16 decimal. 
     
     
       11. A method for generating additive combinations of PCM voice samples as claimed in claim 10, said step of first converting including the steps of: third separating said first PCM voice sample in compressed PCM form into a segment value and a step value;   negating said step value to form a resultant value;   adding 16 decimal to said resultant value;   shifting said resultant value left by 7 minus said segment value times; and   providing said shifted resultant value for said step of combining.   
     
     
       12. A method for generating additive combinations of PCM voice samples as claimed in claim 10, said step of second converting including the steps of: third separating said second PCM voice sample in compressed PCM form into a segment value and a step value;   negating said step value to form a resultant value;   adding 16 decimal to said resultant value;   shifting said resultant value left by 7 minus said segment value times; and   providing said shifted resultant value for said step of combining.   
     
     
       13. A method for generating additive combinations of PCM voice samples as claimed in claim 10, said step of third converting including the steps of: fifth determining a segment value of said third PCM voice sample, in linear form;   third obtaining a step value, said step value being the right adjacent 4-bits to said segment value;   negating said step value to produce a resultant value;   third combining said segment value and said resultant value; and   providing said combined segment value and resultant value for said step of second combining.   
     
     
       14. A method for generating additive combinations of PCM voice samples as claimed in claim 13, said step of fifth determining including the steps: shifting said magnitude value portion of said third PCM voice sample, in linear form, to the left by one bit position;   third incrementing a segment value count by one;   testing a left most bit position for a logic one; and   third iterating said steps of shifting, third incrementing and testing until said logic one bit position is determined.